How can I talk about something really hard - and get people to listen?

We all know that difficult topics can make for difficult conversations... how do we make that easier? How do we make sure that we give ourselves the best chance of a productive chat, where everyone feels better and you can actually resolve an issue... or at least make some headway? When's the best time to tackle something tricky? Is it when we feel like our blood is boiling and we can't rest until we sort something (or somebody!) out? Would we train our dog in that state of mind??